The 3rd Generation Partnership Project (3GPP) employs Orthogonal Frequency Division Multiplexing (shorted for OFDM) and Multiple-Input Multiple-Output (shorted for MIMO) technologies in Release7 to complete the future evolution path HSPA+ of High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA). The HSPA+ is an enhancement technology of the 3GPP HSPA (including HSDPA and HSUPA). The HSPA+ provides a way of smooth evolution from HSPA to Long Term Evolution (LTE) with low complexity and low cost for HSPA operators.
Compared with HSPA, in HSPA+ system architecture, functions of the Radio Network Controller (shorted for RNC) are given to the Node B to form completely flat radio access network architecture, as shown in FIG. 1. In this case, the Node B integrating all functions of the RNC is called the evolved HSPA Node B, or shorted for enhanced Node B (Node B+). SGSN+ is the upgraded Service General Packet Radio System (GPRS) Support Node (SGSN) which can support the functions of the HSPA+. ME+ is the user terminal equipment which can support the functions of the HSPA+. The evolved HSPA system can use the air interface of the version of 3GPP Rel-5 and later, without having any modification for HSPA services of the air interface. After this solution is employed, each Node B+ becomes a node equivalent to the RNC, and has an lu-PS interface to be able to directly connect with a PS Core Network (CN) (as SGSN and GGSN shown in FIG. 1). The lu-PS user plane ends at the SGSN. In the above, if the network supports a direct tunnel function, the lu-PS user plane may also end at the Gateway GPRS Support Node (GGSN). Communication between the evolved HSPA Nodes B is performed through an lur interface. Node B+ has the capability of independent networking, and supports complete mobility functions, including inter-system and intra-system handoff.
As the network is flattened, the user plane data may reach the GGSN directly without passing through the RNC. It means that the ciphering and the integrity protection function of the user plane must be moved forward to the Node B+. At present, an HSPA+ security key hierarchy structure is proposed by Ericsson, as shown in FIG. 2. In the above, the definition of Key (K, the root key), Ciphering Key (CK) and Integrity Key (IK) is completely consistent to those in a Universal Mobile Telecommunications System (UMTS). That is, K is a key saved in the Authentication. Center (AuC) and the Universal Subscriber Identity Module (USIM). CK and IK are a ciphering key and an integrity key calculated from K when Authentication and Key Agreement (AKA) is performed between the User Equipment and the Home Subscriber Server (HSS). They are called the traditional keys. In the UMTS, the RNC uses the traditional air interface keys CK and IK to perform data ciphering and integrity protection. As functions of the RNC are all given to the Node B+ in the HSPA+ architecture, both ciphering and deciphering have to be performed at the Node B+. But, the Node B+ is in an insecure environment with low security. Therefore, a key hierarchy similar to the Evolved Universal terrestrial Radio Access Network (E-UTRAN), i.e., the UTRAN key hierarchy, is introduced to the HSPA+. In the UTRAN key hierarchy structure, the air interface key CKU and IKU are the newly introduced keys for the HSPA+, which are derived of the traditional keys CK and IK, and are called the enhanced keys, wherein the enhanced key CKU is used for encrypting the user plane data and the control plane signaling, and the enhanced key IKU is used for performing integrity protection for the control plane signaling.
In a WCDMA system, the concept of SRNC/Drift RNC (DRNC) is produced due to the introduction of the lur interface. Both SRNC and DRNC are logic concepts for certain specific User Equipment (UE). Simply, for a certain UE, the RNC which is directly connected with the Core Network (CN) and controls all the resources of the UE is called the SRNC of the UE; and the RNC which is not connected with the CN and just provides resources for the UE is called the DRNC of the UE. The UE in connected status must have but only one SRNC, and may have 0 or multiple DRNCs.
In a WCDMA system, SRNC relocation is a process in which the SRNC of the UE changes from one RNC to another RNC. According to different positions of the UE before and after the relocation, there can be two types of relocation: static relocation and concomitant relocation.
The condition for static relocation is that the UE accesses but only from one DRNC. As the relocation process needs no participation of the UE, it is also called the UE not-involved relocation. After the relocation, the connection of the lur interface is released, the lu interface relocates, and the old DRNC becomes to the SRNC, as shown in FIG. 3. Static relocation is caused by soft handoff. Due to the lur interface, the relocation starts after all radio links are linked to the DRNC.
Concomitant relocation is a process in which the UE switches to a target RNC from the SRNC by hard handoff and the lu interface changes simultaneously, as shown in FIG. 4. As the relocation process needs the participation of the UE, it is also called the UE involved relocation.
In the HSPA+, as the Node B+ is in a physically insecure environment, it is easy to suffer hostile attack. The security is under threat. While in the traditional UMTS, before and after the SRNC relocation, the Ciphering key CK and the integrity key IK are identical. This may cause that: on one hand, after a certain base station is breached by an attacker, the attacker may derive the security key of the next hop target base station; on the other hand, if the key is leaked or illegally obtained by an attacker, the attacker may monitor communication of the user all the time, and may also counterfeit data transmission between the user and the network; both situations will cause that the communication security of the user cannot be guaranteed.